Hiroyuki Mitamura

Field-Induced Magnetic Transitions in the One-Dimensional Compound Ca3Co2O6.

Magnetization measurements on the one-dimensional oxide Ca 3 Co 2 O 6 having a triangular net of Co 2 O 6 chains have been carried out both in static and pulsed high magnetic fields. The M / H vs. T curve obeys the Curie-Weiss law at high temperatures. Below 25 K, however, M / H increases abruptly, and a plateau is observed at 1/3 of the full moment in the M - H curve, suggesting a ferrimagnetic state of the ferromagnetic chains due to the antiferromagnetic interchain interaction. At low H , this system is considered to be in a partially disordered antiferromagnetic state for 10 K< T <25 K and in a ferrimagnetic state below 10 K. The observed plateau in the M - H curve for T ≤5 K is broader than for 10 K≤ T ≤20 K, indicating spin freezing at lower temperatures. The results can be discussed in terms of the triangular Ising spin systems.

Faraday force magnetometer for high-sensitivity magnetization measurements at very low temperatures and high fields

A Faraday force magnetometer has been developed for static magnetization measurements at very low temperatures down to 100 mK and in fields up to 9 T. The magnetic force acting on a specimen located in the adiabatic vacuum chamber of a dilution refrigerator is detected by a newly designed load-sensing variable capacitor. Use of a superconducting magnet with gradient coils enables accurate measurement of magnetic moment with a resolution of better than 1×10-7 Am2 ( 1×10-4 emu). An application to magnetization measurements on the heavy-electron antiferromagnet CeB6 is presented.

High-Field Magnetization Processes of Double Spin Chain Systems KCuCl 3 and TlCuCl 3

High-field magnetization processes of S =1/2 double spin chain systems KCuCl 3 and TlCuCl 3 have been measured up to 39 T at 4.2 and 1.7 K for both systems and at 1.0 and 0.5 K for TlCuCl 3 using s...

Magnetization plateaus in NH4CuCl3

The magnetic susceptibility and high-field magnetization process of NH 4 CuCl 3 with double chains of CuCl 3 have been measured using single crystals. No anomaly indicative of the three-dimensional ordering is observed in susceptibility data above 1.7 K. It is found, by magnetization measurement down to 0.5 K, that in contrast to KCuCl 3 and TlCuCl 3 , NH 4 CuCl 3 has a gapless magnetic ground state at zero field. It is observed that the magnetization curve has two plateaus at one-quarter and three-quarters of the saturation magnetization, irrespective of the external field direction. The origin of the plateaus is attributed not to the magnetic anisotropy, but to the quantum effect. The relation between the plateaus and the period of the spin state is discussed in terms of a recent theory presented by Oshikawa et al . [Phys. Rev. Lett. 78 (1997) 1984].

Anomalous magnetizations in single crystalline SrCu2(BO3)2

The magnetic properties of a two-dimensional spin-gap compound SrCu 2 (BO 3 ) 2 , realizing the Shastry-Sutherland model, were investigated using high-quality single crystals. The analysis of the temperature-dependent magnetic susceptibility revealed a spin gap of 34 K. The magnetization curve at 0.4 K possibly has, in addition to the already established one-quarter and one-eighth plateaux, another quantized plateau at one-tenth of the full Cu moment, which is one of the plateaux predicted by Miyahara and Ueda.

Evidence of unusual Kondo effects in dilute uranium compounds UxTh1−xRu2Si2(x⩽0.07)

Abstract Single-site properties of 5f-electrons in URu 2 Si 2 have been studied by means of magnetic susceptibility ( χ ), specific-heat ( C ) and electrical resistivity (ϱ) measurements on U x Th 1− x Ru 2 Si 2 single-crystals in the uranium dilute region ( x ⩽0.07). Anomalous In T -dependence has been found in χ , C and ϱ at low temperatures, suggesting an unusual Kondo effect.

New Megagauss Laboratory of ISSP at Kashiwa

New facilities for megagauss field generation have been built at the Megagauss Laboratory (MGL) of the Institute for Solid State Physics in the new campus of the University of Tokyo at Kashiwa. The MGL moved from the old campus at Roppongi to the new campus in 1999. The new facilities include those for electromagnetic flux compression, the single-turn coil technique, and non-destructive long-pulse magnets with installation of several different capacitor banks. The new facilities aim at producing very high pulsed fields in the megagauss range, up to 750 T and applying them to a variety of experiments for solid-state physics.

Anisotropic Cooperative Jahn-Teller Effect and Metamagnetism in PrCu2

We have studied the origin of the cooperative Jahn-Teller effect and the metamagnetic transition in the orthorhombic compound PrCu 2 . We have determined the anisotropic ferroquadrupole phase diagram by measuring the specific heat and thermal expansion under magnetic fields. With increasing the field, the Jahn-Teller transition temperature increases slightly for the field along a - and c -axes, while it decreases intensively along the b -axis. The phase diagram can be explained quantitatively by including the quadrupolar interaction of - K JT O x y in the crystalline electric field and Zeeman Hamiltonian. The metamagnetic transition, which brings about the conversion between the easy ( a )- and hard ( c )-axes magnetization, has been also studied through the magnetostriction. This phenomenon is also explained quantitatively on the basis of the quadrupolar interaction of - K M O 2 2 . The sign of is found to be negative in the state where the c -axis is the hard one, while it ...

Observation of Magnetic Transition in Quantum Nanomagnet Mn4Br.

The magnetization of the polycrystalline manganese cluster Mn 4 Br was measured down to 0.13 K under a magnetic field of ±15 kOe. It shows a gradual drop at around 1.5 K and the heat capacity measurement at 0 kOe reveals a sharp anomaly at 1.33 K, indicating the occurrence of a second-order antiferromagnetic (AFM) phase transition. The M – H curve well below the transition temperature T N shows a step around 2.5 kOe, which probably corresponds to the transition from the AFM phase to metamagnetic (MM) phase. The observed field agrees with that estimated from T N for the MM transition, using a simple molecular field theory. This is the first observation of a well-defined AFM and also a MM phase among the many manganese clusters with a high-spin ground state that function as molecular nanomagnets.

High-Field Magnetization and Neutron Diffraction Studies of One-Dimensional Compound Ca3CoRhO6

High-field magnetization and neutron diffraction measurements were performed on the one-dimensional compound Ca 3 CoRhO 6 . The long-range ordered state was first observed below 90 K. A plateau at 1/3 of the saturation magnetization was observed in the magnetization curve at 70 K, indicating ferrimagnetic alignment of the ferromagnetic Ising chains. We also observed a large hysteresis originating from a spin freezing of ferromagnetic chains in the magnetization curve at 4.2 K. Based on the results of high-field magnetization and neutron diffraction measurements, a possible magnetic structure is discussed in terms of the spin frustration on the triangular lattice.